Wave repeating and amplifying



July 23, 1929. HElSlNG 1,722,08g

WAVE REPEATING AND AMPLIFYING Ori inal Filed A ril 15, i925 Patented July 1929.

v UNITED "STATES PAr-ENr-oFrIgIE} BAYMOND'A. HEISING, or MILLIBURN, NEW JERSEY, ASSIGNOR re WESTERN ELEC- e eomrA Y, INCORPORATED, oE' NEW 2031:, N. Y., A coRroEa rIoN on EW you;

Thepresentinvention relates to wave repeating or wave amplificat1on. The invention has particularv application 1n connection with discharge tube repeaters or similar de- 5 vices possessing appreciable capacity between their elements, due to which capacity there is a tendency for the waves to be shunted across the circuit or passed directly from the input side to theoutput side of the device, or in the q reverse direction, by condenser action.

lt-is an object of the invention to compensate for this tendency of the waves to pass by condenser action between elements of the repeating device or circuit.

Since this tendency becomes greater at the higher frequencies, the'invention has particular value in radio frequency circuits, although it is applicable in general to repeatlng systems or devices operating at any desired frequencies.

A further object of the invention is to compensate for the capacity eifects of a discharge tube repeater in causing or aiding the production of oscillations in the circuit or circuits associated with the tube.

A further object of the invention is to compensate for the reactive eifect of tuned circuits or tuning elements or'reactive elements in general, associated with the output side of a discharge tube repeater upon the input circuit, or upon circuits associated with the input side of the tube, due to back coupling through the tube.

A still further object of the invention is to stabilize a radio frequency amplifying circuit so that more dependable action and greater amplification can be obtained with the circut than has heretofore been obtainable.

Briefly and specifically stated, the invention involves the balancing out or neutralizing of the potential variations present at a particular point in the repeater circuits in consequence of the undesired condenser action or capacity transfer of potentials between elements of the repeating device or circuits; This is preferably accomplished, ac-

cording to the invention, by providing a condenser at such a point in the circuit that the potential variationsacross itare similar to the undesired. potential variations set up by the capacity between elements of the repeat-- er, and opposing the potential variations across the condenserto the undesired variations.

WAVE REPEATING AMPLIFYING.

t t-dean am A ril 13,1923, Serial No. 681,814.' Renewed February 12, 1929.

The above and other objects ofthe invention, and the various features which contribute toward the realization of the objects will be explained more fully in the following description, and by the aid of the accompanying drawings, in which: Figs. 1 and 2 show diagrams of balanced orbridged circuit arrangements which are helpful in explaining the action of the circuits according to the invention; Figs. 3, 4, and 5 are typical circuit applications of the invention; and Figs. 3 and 4 show modified arrangements.

Figs. 1 and 2 will be referred to in connection with the circuit arrangements shown in Figs. 3 and 4, respectively. Fig. 3 shows a single stage'amplifying orrepeating circuit embodying the invention. This repeating circuit is inserted between the incoming circuit I and the outgoing circuit II. The repeating circuit includes the electric discharge tube 1 of familiar type, together with the windings andother circuit elements shown. This tube comprises a preferably highly-evacuated envelope in which are included a. heated filament or cathode f, a cold electrode or anode P commonly called the plate, and the control electrode or grid 9, all suitably positioned with respect to one another. It is well known that a certain capac ity exists between the grid and plate, its magnitude depending on their areas, proximity,

etc., and this may be denoted by the symbol C Similarly a capacity C exists between the grid and filament, and another-capacity Opf exists between the plate and filament. These capacities are, in the case of the usualamplifying or repeating tube, relatively small compared to the condensers commonly employed in the circuits. However, these capacities are in many cases sufiicient to influence the action of the tube or device in repeating and amplifying waves, and this influence is most marked at relatively high fre-' quencies such as radio frequencies.

One efiect of these internal capacities, for example, is to cause or aid the production of self sustained oscillations, sometimes referred to as singing. A disturbance in the plate circuit, for example, changes the potential of the plate,'and due to the capacity C the grid potential is correspondingly changed. This change of. grid potential affects the current flow through the tube. which again changes the plate potential, and if the potential variations so impressed on the grid and plate are of the proper sign and magmtude, sustained oscillations, or singing, will.

' a serious limitation on the amount of amplification obtainable in such circuits.

Another common effect of the internal capacity of a tube is to permit a reactive efiect of elements in the output circuit on the input circuit. For example, in transmitting circuits an oscillator is often connected to an amplifier, which, in turn, feeds into a tuned transmission circuit such as an antenna or a selective branch to a line. Where the period of the oscillator depends upon a tuning of its circuit it has been found that a change of tuning of the antenna, for example, or a change in coupling, or any change which disturbs the adjustment of the circuit, may react through the tube to change the period of the oscillator. The two effects above-specifically pointed out are t pical and may be taken as examples.

- These e ects, and various others, are or may be present unless some balancing or compensating arrangements are employed to counteract them. Three arrangements illustrative of the principle employed in the invention will nowbe described.

In the arrangement of Fig. 3, waves in the incoming circuit I set up potential variations across the windings 4 and 5, the potential of the lower end of winding 5' at any instant being opposite in sign to that of the upper end or winding 4 at the same instant. The potential across winding 4 is effective in controlling the potential of the grid with respect to the cathode, and such grid potential controls in the well known manner the current in the anode circuit and hence the current in the outgoing circuit II. The winding 5 is not efi'ective in controlling the grid potential in accordance with the waves to be repeated but 4 its purpose will be explained below in connection with the balancing out or neutralizing of the tendency for the device 1 to transfer waves by effects other than control of the space current by the grid potential, the princ1 al other effect being that of the capacity which the elements of the device 1 exhibit toward one another. a

For the purpose of explaining the balancing action of the circuit scheme of Fig. 3, this circuit may be reduced to-the brid e diagram of Fig. 1. Thexwindings-4 an 5 are preferably very closely coupled with each other, so that any flux variation in one causes a corresponding flux change in the other. The directions of the fluxes in these windings is such that if afcurrent impulse is setu from 8 to 9, this acts to set up a'correspon ing current im ulse from 9 to 10. If, therefore, the impu se of current from 9 to 10 is opposed, this is equivalent to opposing the unpulse of current from 8 .to 9. Any change of potential in the to the point 8 wit respect to the point 9, therefore, isneutralized if an ual positive potential change is'applied to t e point 10, and the same is, of course, true of negative potentials. This means that, as regards variation's'of-potential, the grid .will have, at any instant the same potentlal as the filament if the point 10 has the same potential as the point 8, for as stated above, any tendencyfor nomena such as singing and the like would be liable to occur as explained heretofore. According to the invention, however, the winding 5 is provided and the balancing condenser 2, the'former serving to cooperate with the winding 4 in the manner described, and the latter being of such dimensions as to balance the capacity C The assumed change in plate potential, therefore, produces the same potential change at point 10 as is produced on the grid by the capacity C and, due to the relation between windings 4 and 5, the points 8, 9 and 10 are all maintained at the same potential so far as the influence of the plate po-.

tential variations is concerned. Since the late potential changes are thus prevented rom setting up differences of potential be-' tween the grid and filament, the undesired eii'ects mentioned are prevented from' occurring. a

A more complete balance can be obtained lpositive direction applied by inserting the condenser 3 as shown, this condenser being of the pro or dimensions to balance the capacity C is condenser is not so important, however, as the balancing elements 2 and 5, and it can in many cases be dis ensed with.

en the tube 1 is employed to repeat variations of any kind, these variations occur between the filament and plate as variations in the space current, and the bridge diagram of Fig. 1 to be complete must include the fictitious alternating current generator 7 and the condenser C,,,, the plate impedance of the tube being assumed to be in the generator 7. The efiect which these elements between the filament and plate might produce on the grid otential differences across the points a P ment being indicated in Fig. 2.. This ar-v rangement offers more difiiculties'than the arrangement of Fig. 3, and requires greater accuracy of balance to secure the same results. The principal balancing elements are the condenser 14, which is so dimensioned as to balance the capacity C and the winding 13 which preferably has as nearly-perfect mutual relation as possible, that is, as high degree of coupling as possible, withthe wind ing 12. Windings 12 and 13 cooperate in the manner described in detail in connection with the windings 4 and 5 of Fig. 3, so that a potential difference set up between the plate and filament, that is, bet-ween 18 and 19, 1s accompanied by an equal potential difference between 19 and 20. j The effect of potential changes on the plate is therefore to produce equal but opposite potential changes at 20, and if the capacity 14 just equals the capacity (3 the influence of these two potential variations on the potential of the grid Wlll be nil. The potential of the grid with respect to the filament is, therefore, uninfluenced by plate potential variations.

The space current path and the plate 1mpedance are, inthis type of circu1t, 1n one of the arms of the bridge rather than in a diag- 'onal branch, and it is therefore necessaryto balance the effects on the grid of the var1ations taking place between the filament and plate and representing the wave that is being repeated; In this type of circuit 1t1s more important to maintain. an accurate balance between the capacities C and 15 than was necessary in the arrangement of Figs. 1 and 3, and it may be desirable also to provide an impedance 16 to match the impedance 16' of the tube. However, these elements are less important than the elements 13 and 14, and may in'cases involving small power he omitted or supplied with approximate values. On account of the larger currents carried by the coils 12 and 13, they should be balanced with accuracy. 7

The balancing circuits do not interfere 1n any way with repetition of waves from the circuit I to the circuit II, and such repetition may take place in the circuits described,

with or without amplification, as desired, in accordance with the generally well-understood action of such devices. Either arrangement'represented in Figs. 3 and 4 may be preceded or followed by other tube anipli fiers, repeaters, or the like as may be desired, and may be used for transmitting or receiving or in any other situation where repeaters or discharge tubes are or may be used.

Instead of coupling the incoming circuit I in Fig. 3 or the outgoing circuit 11 in, Fig. 4 inductively to thetube circuit windings, either circuitmay be connected as shown by the fragmentary circuits of the respective Figs. 3 and4 the broken lines A--A and 'B--B, respectivel indicating the portions of the circuits of igs. 3 and 4 to be replaced by the alternativecircuits. Fig. 5 illustrates a somewhat different manner of applying the principle employed in the circuit of Fig. 4. Instead of using the balancing coils 12 and 13 to couple to an outgoing circuit II as in Fig. 4, the corresponding balancing coils 12' and 13 of Fig. 5 are I partly in shunt of the grid and plate branches through which the operating waves are transmitted and these coils are used merely for-securing the necessaryexchange 0f voltages between the tube and circuit elements to effect abalance after the manner shown in Fig. 2. By reference to Fig. 2 and with the explanation given in connection with the circuit of Fig. 4, it will be clearhow the plate potential variations are balanced out on the grid.

The generator 25 represents any desired type of transmitting source, and the waves to be transmitted are impressed on the grid of the repeater or amplifier 1; through transformer 27, the repeated amplified waves passing mainly through the large condenser 28 and'through the inductive coupling into the antenna 26. Changes in adjustment or inthe characteristics of the antenna are prevented from disturbingthe generator 25 or other circuits associated with the grid circuit of the tube. This is due to the fact that potential variations set up on the plate from the circuits associated with the plate are prevented from appearing in the grid circuit by the balancing action of condenser 14 and windings 12 and 4. Generator 25 may have a sensitive frequency adjustment and its period may, as in the case of oscillating. discharge tube generators, be determined by a resonant circuit V 13' as described in connection with Figs. 2 and If desired, the outgoing or load circuit. may be coupled to the coils 12'and 13 instead of as shown in Fig. 5.

It has been stated that the capacities2, 14,

3, etc, are made equal to the capacities which they are used to balance. This is preferable but is not to be construed as limiting the inverition, since the only requirement of these capacities is to reduce the degree of balance which any particular conditions require, and these capacities may actually difi'er considerably from the tube capacities, particularly where the windings 4 and-5 or 12 and 13 may be unequal or notcloselycoupled or where other circuit conditions might require that these capacities have ,a 'difierentvalue from exact equality with the tube capacities in order to obtain a balance. The same is true of device for repeating potential variations, having an input and an output electrode between which appreciable capacity exists, an output circuit for transmitting the variations repeated by said device, means for coupling said device to said output circuit, means independent of the coupling means for deriving potential variations from said output electrode substantially equal in amplitude and opposite in phase to the variations repeated, and a condenser connected between the potentialderiving means and said input electrode, said condenser having a capacity substantially equal to the capacity between said electrodes 2. In a repeating system, a repeating device having input and output electrodes between which appreciable capacity exists, a load circuit, means for coupling said device to said load circuit, and means for neutralizing the potential variations set up on said input electrode by potential variations on said output electrode and due to the capacity between said electrodes, said means comprising a condenser connected to said input electrode and a pair of mutually related inductance windings separate from said coupling means for deriving from the output electrode. and applying to said condenser, potential variations of opposite phase to the potential variations on said output electrode.

3. In a transmission system, a generator, a transmitting conductor, a discharge tube for repeating wavesfrom said generator to the transmitting conductor, a transformer for impressing the waves from the generator on said conductor, and means external to the discharge tube and separate from and independent of said transformer" for preventing maaoee changes in the characteristic of the transmitting conductor from reactin through the inherent capacity of the discharge tube upon the generator.

4. In a radio transmitter, a source of radiofrequency waves, an amplifier for said waves comprising a discharge tube having input and outputelectrodes between which appreciable capacity exists, an antenna, a radio frequency transformer for impressing waves from'said amplifier upon said antenna, and means separate from and independent of said transform er for neutralizing the effect of the capacity of the .tube to prevent the frequency of said source from changing due to a change in adjustment of the antenna.

5.In a wave repeating system, a repeating device for repeating potential variations, having an output electrode and input electrodes between which appreciable capacity exists, an output circuit for transmitting the variations repeated by said device, means for coupling said device to said output circuit, means independent of the coupling means for deriving potential variations from said output electrode substantially equal in amplitude and opposite in phase to the variations repeated, a condenser connected between the ,7

potential-deriving means and one of said input electrodes, said condenser having a capacity substantially equal to the capacity between said output electrode and said one input electrode, and a second condenser connected between said potential-deriving means and the other of said input electrodes.

6. In a transmission system, a source of waves, an amplifier for said source, comprising a space discharge device having input and output electrodes between which appreciable capacity eiiect exists, and having an input and an output circuit, a load circuit associated with said output circuit, means included in said input circuit for impressing waves to be repeated on said input circuit, and means vindependent of the nature of said load circuit for preventing variations in the waves transmitted through said device due to said natural capacity between said in ut and output electrodes from reaching sai load circuit comprising an inductance in shunt to a portion of said input circuit, and separate and distinct from said means for impressing the waves on the input circuit, a second inductance coupled to the first mentioned inductance in shunt to a portion of said output circuit, and capacit substantially equal to the natural capacitylietween said lnput and output electrodes, connected between said input electrodes.

7. In a wave repeating system a space dis charge device having a cathode an anode and a grid or control element, a source of waves to be repeated associated with the grid and cathode, said cathode having a preclable capacitywith 'respect to said ano e, and means to neutralize the efi'ect of said capacity comprising means for deriving from said anode a potential substantially equal and opposite at all times to the instantaneous potential of said anode with respect to said cathode, and a capacity substantially equal to the cathode-anode capacity having one terminal connected to the cathode and its other terminal connected to said means to receive therefrom said equal and opposite potential.

8. In a Wave transmission system, a source of waves of varying potential, a repeating device having an input circuit and an output circuit, and having an input electrode and an output electrode between which appreciable natural capacity exists, means coupling said source of waves to said input circuit whereby potential variations are supplied to said device to be repeated, an outgoing circuit,

means coupling said output circuit to said outgoing circuit whereby the variations repeated by said device are transmitted thereto, means independent of said input circuit coupling means and said output circuit coupling means for deriving potential variations from said output electrode substantially equal in.

amplitude and opposite in phase to the variations repeated, means for supplying the derived variations to said input electrode, and a condenser connected between the potentialderiving means and said input electrode, said condenser having a capacity substantially equal to the natural capacity between said input electrode and said output electrode.

In Witness whereof, I hereunto subscribe my name this 12th day of April, A. D. 1923.

RAYMOND A. HEISING. 

